Method of making racket cord



3,024,589 METHOD OF MAKING RACKET CORD George Vaughan, Sawbridgeworth, England, assignor to Dunlop Rubber Company Limited, London, England, a British company Filed Mar. 6, 1956, Ser. No. 569,765 9 Claims. (Ci. 57-162) This invention is a continuation-impart of my co-pending application Ser. No. 473,922 filed December 8, 1954, and now abandoned, and relates to cords and in particular to cords used for the stringing of rackets for tennis, badminton and the like and to a method of making them.

It is the object of the present invention to provide a cord suitable for stringing a tennis or like racket which is of satisfactory performance and appearance.

The properties required in cords if they are to be satisfactory for stringing rackets are such that of the natural filamentary materials, only natural gut has found general acceptance. Gut is, however, very expensive and many attempts have therefore been made to produce cords from synthetic filamentary materials. None of the substitutes so far proposed, however, has all the properties required and natural gut is still considered to be the only satisfactory cord for use in high quality rackets.

The present invention is based on the discovery that racket cords which are as good as natural gut can be produced from materials made of a synthetic fibre-forming polymer having the formula R.X.R .Y. where R and R are hydrocarbon radicals and X and Y are amide or ester radicals, provided that the cord is built up in a particular manner from the component materials and that the materials are bonded together by means of a special adhesive. In this manner cord can be produced which does not stretch or wear unduly when subjected to continued impact with a ball, so that rackets equal in properties to those strung with natural gut can be obtained. The polymers which give the best results are polyhexamethylene adipamide, the polymer obtainable from amino-caproic acid and polyethylene-terephthalate.

The production of cord in accordance with the present invention is carried out by spirally wrapping a filamentary core with one or more layers of wrapping material, both the core and the wrapping material being made of a fibre forming polymer as defined above, and bonding the wrapping to the core by means of an adhesive containing a high concentration of a phenol together with alcoholsoluble nylon. The best results are obtained with phenol itself, i.e. monohydroxybenzene, but other phenols which have a softening action on the polymer, e.g., cresol, a xylenol or resorcinol, may be employed.

The phenol concentration should be between 40% and 80% and the nylon concentration between 10% and 40%. In addition the adhesive may contain up to 40% of an alcohol, particularly methyl, ethyl or benzyl alcohol. After winding the cord is heated to drive off the solvent and simultaneously is slightly stretched.

The helix angle of the spiral wrapping is of importance in obtaining cord having the required properties. In general it should be between 30 and 70 and is preferably about 40 to 50.

The best cord is obtained by using a single monofilament of heavy denier, e.g., about .03" diameter, as a core and wrapping it with two layers of opposite hand of monofilaments having a diameter of about .006". A cord of somewhat lower quality, though still capable of giving satisfactory results, is obtained if a number of strands of multifilament yarn, e.g., of 210 denier, are used for the core and wrapping instead of the monofilaments.

The invention will now be more particularly described with reference to a preferred method of producing cord ice suitable for stringing a tennis racket, and illustrated in the accompanying diagrammatic drawings wherein:

FIGURE 1 shows the steps in forming a cord, and

FIGURE 2 shows the construction of a cord formed by a monofil core wrapped with two layers of monofils.

As shown in FIGURE 1 a nylon monofilament 0.042" in diameter forming a core A and wound on a let-off bobbin 1 of a wrapping machine was passed over tensioning rollers 2 and through a bath 3 containing a bonding solution consisting of 6 parts of phenol, 2 parts of alcoholsoluble nylon and 3 parts of water by weight. The core was then passed upwardly through the wrapping machine represented by the bobbins 4 where it was spirally wrapped with two layers of nylon monofilament 0.005" in diameter. As shown in FIGURE 2 the first layer B was wrapped in an anti-clockwise direction with a ribbon of 23 filaments and was immediately followed by the second layer C which was wrapped in a clockwise direction with a ribbon having 25 filaments. Excess bonding solution was wiped off at 5 (FIGURE 1) and the wrapped cord D was wound around an intermediate take-off drum 6 mounted above the wrapping machine at a peripheral speed of 27 inches per minute.

Two drying tubes 8 and 9 were used, each consisting of a 10 foot length of heat-resisting glass tubing having an electrical tape heating element wound spirally around the surface and covered by lagging. Each tube was thermostatically-controlled to a temperature of 150 F. at the bottom and graduated to 250 F. at the top end.

The wrapped cord D from the machine was led up the first tube 8. The cord was then passed downwardly through the second tube 9.

On emerging from the second tube the dried cord was wound up on a take-01f drum 7 at a speed of 28% inches per minute, the final gauge of the cord being 0.058".

The physical properties of the cord Were:

Breaking load lbs Elongation at break percent 45 The impact strength of the cord was of the order of twice that of natural gut.

Cord may be prepared in a similar manner by wrapping a core of nylon or polyethylene-terephthalate with a single layer of nylon or polyethylene-terephthalate in the form of a monofilament 0.005" in diameter.

Preferably the core and the wrappings both have the same chemical composition, e.g. are both made of nylon or both of polyethylene-terephthalate.

The material used may be dyed to a natural gut colour so that cord is obtained which not only is equal in performance to natural gut but is also almost indistinguishable from it in appearance.

Cords may alternatively be made of a core of nylon monofilament or yarn and a wrapping of nylon yarn. A suitable yarn for wrapping is of 210 denier. Such a cord is also suitable for stringing a racket but its appearance and durability are not as good as that of the cords described above made wholly of nylon monofilaments.

An alternative construction may be obtained by covering a core, consisting, e.g. of a nylon monofilament of 0.010" in diameter, with a series of alternate clockwise and anti-clockwise wrappings of 0.005 diameter nylon monofilament, the number of wrappings being such that the finished diameter of the cord is between 0.020 and 0.060.

The core is treated by the application of the phenolic adhesive before each pair of wrappings is applied.

Instead of using individual monofilaments or yarns as the wrapping material a number of monofilaments or yarns adhered together to form a tape about wide may be used, as may a tape obtained by extrusion or by cutting from sheet materials. The advantage of using a wrapping material in tape form is that wrapping can be carried out much more rapidly than if a number of monofilarnents or yarns fed from separate packages are employed.

Having now described my invention, what I claim is:

1. A method of making a racket cord which comprises coating a core having a diameter of from 0.020 inch to 0.060 inch of textile material made of a synthetic fibre-forming polymer having the formula RXR Y, where R and R each represent hydrocarbon radicals and X and Y represent a radical selected from the group consisting of amide radicals and ester radicals, with a liquid adhesive containing from 40% to 80% of a phenol and of from 20% to 40% of alcohol-soluble nylon, spirally wrapping thereon at least one layer of a wrapping material applied as a ribbon of filaments at an angle of from 30 to 70 with respect to the longitudinal axis of the core and made of a synthetic fibre-forming polymer having the formula RXR Y wherein R, R X and Y have the meanings given above, heating the wrapped cord to a temperature between 150 F. and 250 F. until the phenol is substantially removed therefrom and simultaneously stretching the cord.

2. A method according to claim 1 wherein the phenol employed is monohydroxybenezene.

3. A method according to claim 1 wherein the liquid adhesive contains from 40% to 80% of monohydroxybenzene, from to 40% of alcohol-soluble nylon and an alcohol in an amount not exceeding 40%.

4. A method according to claim 1 wherein the polymer is polyhexarnethylene adipamide.

5. A method of making a racket cord having a diameter of from 0.020 inch to 0.060 inch which comprises coating a core of textile material made of a synthetic fibre-forming polymer having the formula RXR Y, Where R and R each represent hydrocarbon radicals and X and Y each represent a radical selected from the group consisting of amide radicals and ester radicals, with a liquid adhesive containing from 40 percent to 80 percent of a phenol and of from percent to 40 percent of alcohol soluble nylon, spirally wrapping thereon at least an inner layer and an outer layer of a wrapping material applied as ribbons of filaments at an angle of from to 70 with respect to the longitudinal axis of the core and made of a synthetic fibre forming polymer having the formula RXR Y, where R, R X and Y have the meanings given above, adjacent layers of wrapping material being wrapped one in clockwise and the other in anti-clockwise direction, Wiping excess adhesive from the outer layers and heating the wrapped cord to a temperature in the range of from 150 F. to 250 F. until the phenol is substantially removed therefrom and simul taneously stretching the cord.

6. A method according to claim 5 wherein the synthetic fibre forming polymer of the core and of the wrapping material is nylon.

7. A method according to claim 5 wherein the angle of wrap is from to 8. A method according to claim 1 wherein two or more wrapping layers are wound on the core, adjacent layers being wrapped one in clockwise and the other in anti-clockwise direction.

9. A method according to claim 1 wherein the angle of wrap is from 40 to 50.

References Cited in the file of this patent UNITED STATES PATENTS 2,205,144 Kaplan June 18, 1940 2,302,332 Leekley Nov. 17, 1942 2,312,879 Christ Mar. 2, 1943 2,392,842 Doell Jan. 15, 1946 2,401,291 Smith May 28, 1946 2,735,258 Crandall Feb. 21, 1956 2,824,485 Gregory Feb. 25, 1958 OTHER REFERENCES American Handbook of Synthetic Textiles (Mauersberger), published by Textiles Book Publishers (New York, NY), 1952; page 248 relied on. 

1. A METHOD OF MAKING A RACKET CORD WHICH COMPRISES COATING A CORE HAVING A DIAMETER OF FROM 0.020 INCH TO 0.060 INCH OF TEXTILE MATERIAL MADE OF A SYNTHETIC FIBRE-FORMING POLYMER HAVING THE FORMULA RXR1Y WHERE R AND R2 EACH REPRESENT HYDROCARBON RADICALS AND X AND Y REPRESENT A RADICAL SELECTED FROM THE GROUP CONCONVEYOR BAND AND MOVABLE DOWNWARDLY INTO A CIGARETTE FRAME HAVING A FRONT WALL AND A REAR WALL, SAID SUPPORT MEANS BEING ADAPTED TO BE WITHDRAWN FROM UNDER THE CIGARETTES TOWARDS THE END OF ITS DOWNWARDLY FROM MOVEMENT, GUIDE MEANS EXTENDING DOWNWARDLY FROM SAID DISCHARGE END OF THE CONVEYOR BAND TO RETAIN THE CIGARETTES ON SAID SUPPORT MEANS DURING THE MOVEMENT OF SAID SUPPORT MEANS DOWNWARDLY TOWARDS AND INTO SAID CIGARETTE FRAME, AND MEANS FOR CAUSING SUBSTANTIALLY HORIZONTAL RELATIVE MOVEMENT BETWEEN SAID SUPPORT MEANS AND SAID CIGARETTE FRAME IN A DIRECTION TO ENLARGE THE SPACE BETWEEN SAID SUPPORT MEANS AND THE FRONT WALL OF THE CIGARETTE FRAME AND THEREBY TO ACCOMODATE AN INCREASNG NUMBER OF CIGARETTES BETWEEN SAID SUPPORT MEANS AND SAID FRONT WALL UNTIL SAID SUPPORT MEANS IS WITHDRAWN UPWARDLY IN THE VICINITY OF THE REAR WALL OF THE CIGARETTE FRAME, THEREBY ENABLING THE CIGARETTES TO ENTIRELY FILL THE CIGARETTE FRAME. 